CVE-2025-53599 is a critical cross-site scripting (XSS) vulnerability identified in the NAVER Whale browser for iOS versions prior to 3.9.1.4206. This vulnerability arises from improper neutralization of input during web page generation, specifically related to the handling of crafted JavaScript schemes. An attacker can exploit this flaw by crafting a malicious JavaScript URI scheme that, when processed by the vulnerable browser, leads to the execution of arbitrary scripts within the browser context. This type of vulnerability falls under CWE-79, which involves improper sanitization or encoding of user-supplied input, allowing injection of executable code. The CVSS v3.1 score of 9.8 indicates a critical severity level, with an attack vector that is network-based (AV:N), requiring no privileges (PR:N) and no user interaction (UI:N), and impacting confidentiality, integrity, and availability to a high degree (C:H/I:H/A:H). The scope is unchanged (S:U), meaning the impact is confined to the vulnerable component. The absence of known exploits in the wild suggests this vulnerability is newly disclosed, but the ease of exploitation and high impact make it a significant threat. Since the vulnerability affects the iOS version of the Whale browser, it targets users on Apple mobile devices. The flaw could be leveraged to steal sensitive information, hijack user sessions, perform unauthorized actions on behalf of the user, or deliver further malware payloads, severely compromising user security and privacy.

For European organizations, this vulnerability poses a substantial risk, especially those with employees or customers using the NAVER Whale browser on iOS devices. The ability to execute arbitrary scripts without user interaction or privileges means attackers can remotely compromise devices, potentially leading to data breaches, credential theft, and unauthorized access to corporate resources. Organizations in sectors such as finance, healthcare, and government are particularly vulnerable due to the sensitive nature of their data and regulatory requirements under GDPR. The exploitation could facilitate lateral movement within corporate networks if compromised devices are used to access internal systems. Additionally, the breach of confidentiality and integrity could result in reputational damage and legal consequences. Given the mobile nature of the affected platform, remote workforces and BYOD policies increase the attack surface. The lack of a patch at the time of disclosure further elevates the risk, necessitating immediate mitigation efforts.

1. Immediate deployment of the updated NAVER Whale browser version 3.9.1.4206 or later once available to eliminate the vulnerability. 2. Until patching is possible, implement network-level controls such as blocking or filtering suspicious JavaScript URI schemes at the perimeter or endpoint security solutions. 3. Educate users about the risks of clicking on unknown or suspicious links, especially those involving JavaScript schemes, to reduce the likelihood of exploitation. 4. Employ mobile device management (MDM) solutions to enforce browser updates and restrict installation of unapproved applications. 5. Monitor network traffic and device logs for unusual activity indicative of exploitation attempts, such as unexpected script execution or anomalous outbound connections. 6. Consider deploying web application firewalls (WAF) or endpoint protection platforms capable of detecting and blocking XSS payloads targeting mobile browsers. 7. Review and tighten access controls and session management policies to limit the impact of potential session hijacking or credential theft.